The present invention relates to an oscillation circuit and a strobe circuit, which employs the oscillation circuit, and which is suitably incorporated into lens-fitted film units.
Conventionally, some of the lens-fitted film units, in each of which a non-exposed film is incorporated in advance of putting them on the market, also incorporate a strobe device, which emits a strobe light from a light emitting tube, such as a xenon lamp, etc., by means of charging/discharging actions of a capacitor when capturing an image.
In the abovementioned lens-fitted film unit incorporating strobe device, a light-emitting action of an indicating lamp, such as a light emitting diode, a neon tube, etc., notifies the user of the completion of the discharging action of the capacitor.
An example of the conventional strobe circuits incorporated in the abovementioned lens-fitted film units will be detailed in the following, referring to FIG. 11.
As shown in FIG. 11, the conventional strobe circuit comprises boosting-up circuit 101 for boosting up a source voltage of battery BT to a predetermined voltage necessary for the light-emitting action of strobe-lighting tube Xe, strobe-lighting circuit 102 for charging main-capacitor MC with the high voltage generated by boosting-up circuit 101 to emit a strobe light from strobe-lighting tube Xe, and neon lamp activating circuit 103 for activating the illumination of neon lamp NE, either when charging operation for main-capacitor is completed or when the user forgets to turn off a strobe-switch operating section (not shown in the drawings), mounted in the lens-fitted film unit, so as to warn the user.
Battery BT is coupled to boosting-up circuit 101 through switch SW1 (a power switch), which is one of main switch MSW, serving as a double-pole single-throw switch, to be turned on or off by the operating action for the strobe-switch operating section.
The boosting-up circuit 101 comprises oscillation transistor Q, oscillation transformer TR1 and resistor R1.
Oscillation transformer TR1 is composed of primary winding W1 and secondary winding W2 for boosting up the voltage of battery BT. Oscillation transistor Q and oscillation transformer TR1 constitutes a self-running blocking oscillator, which starts oscillating action by turning on main switch MSW and continues its oscillation under the direct current fed from battery BT, so that an alternate current flowing through primary winding W1 induces an alternate high-voltage, corresponding to the winding number ratio of primary winding W1 and secondary winding W2, at both terminals of secondary winding W2.
Secondary winding W2 of oscillation transformer TR1 is coupled to main-capacitor MC (for instance, an electrolytic capacitor) and trigger-capacitor TC, included in strobe-lighting circuit 102, through rectifying diode D, so that the rectifying diode D rectifies alternate high-voltage induced in secondary winding W2 and the rectified current flows into main-capacitor MC and trigger-capacitor TC to charge them.
Strobe-lighting circuit 102 comprises main-capacitor MC, strobe-lighting tube Xe, trigger-switch TSW, which turns on and off in conjunction with movements of shutter blinds, trigger-coil TR2 composed of primary winding W11 and secondary winding W12, resistor R2, trigger-capacitor TC, neon lamp NE, which emits a light when the charge voltage of main-capacitor MC reaches a predetermined voltage, and resistor R4 serially connected to neon lamp NE.
Cathode K and anode A of strobe-lighting tube Xe are coupled to negative pole (xe2x88x92) and positive pole (+) of main-capacitor MC, respectively, and gate G is coupled to secondary winding W12 of trigger-coil TR2.
Further, the strobe circuit comprises oscillation stoppage circuit 104 for stopping unnecessary oscillating action of transistor Q when main-capacitor MC is completely charged and for stopping the power supply to boosting-up circuit 101 from battery BT.
Oscillation stoppage circuit 104 comprises oscillation-suppressing transistor Q11, resistor R11, and zener diode ZD.
The emitter and the collector of oscillation-suppressing transistor Q11 are coupled to the base of oscillation transistor Q and switch SW2 of main switch MSW, respectively, while the high-voltage generated by boosting-up circuit 101 is applied to the base of oscillation-suppressing transistor Q11 through zener diode ZD and resistor R11.
The operations of the abovementioned strobe circuit, mainly the operations of oscillation stoppage circuit 104, will be described as follow.
When turning on switch SW1 and switch SW2 by operating main switch MSW, oscillation transistor Q starts to oscillate, and the high-voltage, boosted by boosting-up circuit 101, charges main-capacitor MC.
At the same time, the high-voltage, boosted by boosting-up circuit 101, is applied to zener diode ZD.
When the charged voltage of main-capacitor MC exceeds the zener voltage of zener diode ZD, zener diode ZD turns on, resulting in a conductive state of oscillation-suppressing transistor Q11. Then, oscillation transistor Q turns off, since the conductive state of oscillation-suppressing transistor Q11 lowers the base potential of oscillation transistor Q, the base of which is coupled to the emitter of oscillation-suppressing transistor Q11.
As a result, the oscillating action of oscillation transistor Q is automatically stopped, and the power supply, fed from battery BT to boosting-up circuit 101, is also cut off to stop the unnecessary charge current flowing into main-capacitor MC. The conventional technology mentioned above is also set forth in Tokkaihei 11-183975.
According to the strobe circuit having conventional oscillation stoppage circuit 104 mentioned above, it is possible to automatically stop the oscillating action of oscillation transistor Q, to prevent excessive charging operation to main-capacitor MC and to prevent unnecessary power dissipation of battery BT when the user forgets to turn off main switch MSW.
In the conventional strobe circuit mentioned above, however, since many parts, including relatively expensive parts such as oscillation-suppressing transistor Q11 and zener diode, are employed for oscillation stoppage circuit 104, there have been problems that man-hours for assembling the lens-fitted film unit and its cost tend to increase.
To overcome the abovementioned drawbacks in conventional strobe circuits, it is an object of the present invention to provide a strobe circuit, which makes it possible to conduct a timer operation (automatic stopping operation after a predetermined time) and/or an intermittent oscillating operation by adding a small number of parts, and which is suitably employed for lens-fitted film units.
Further, it is another object of the present invention to provide a strobe circuit, which makes it possible to restrict an increase of man-hours for assembling it and to prevent a power dissipation of the power source when the user forgets to turn off the main switch.
Accordingly, to overcome the cited shortcomings, the abovementioned objects of the present invention can be attained by a lens-fitted film unit, a strobe circuit and an oscillation circuit, described as follow.
(1) A lens-fitted film unit incorporating a strobe device, comprising: a main body; a photographic film loaded in advance in the main body; a shutter; a photographic lens; and a strobe circuit included in the strobe device, the strobe circuit comprising, a boosting-up circuit including a DC power source, an oscillation transistor, an oscillation transformer having a primary winding and a secondary winding, and a rectifying element for rectifying an electronic current induced at the secondary winding of the oscillation transformer, an oscillation controlling circuit for controlling a base potential of the oscillation transistor, and a strobe lighting circuit including a main-capacitor charged by the electronic current rectified by the rectifying element, and a strobe-lighting tube driven by an electronic charge charged in the main-capacitor, wherein a collector and an emitter of the oscillation transistor are serially coupled between the DC power source and the primary winding of the oscillation transformer, and a base of the oscillation transistor is connected to one end of the secondary winding of the oscillation transformer so as to apply a voltage, induced at the secondary winding, to the base, and the oscillation controlling circuit is coupled between the DC power source and the base of the oscillation transistor.
(2) The lens-fitted film unit of item 1, wherein the oscillation controlling circuit includes a serial connection of a capacitor and a resistor.
(3) The lens-fitted film unit of item 2, wherein a capacitance value of the capacitor is in a range of 1000 pF-100 xcexcF.
(4) The lens-fitted film unit of item 2, wherein a resistance value of the resistor is in a range of 1 Kxcexa9-10 Mxcexa9.
(5) The lens-fitted film unit of item 1, wherein the oscillation controlling circuit includes a serial connection of a second resistor and a parallel connection of a capacitor and a first resistor.
(6) The lens-fitted film unit of item 5, wherein a capacitance value of the capacitor is in a range of 100 pF-47 xcexcF.
(7) The lens-fitted film unit of item 5, wherein a resistance value of the first resistor is in a range of 100 Kxcexa9-4.7 Mxcexa9.
(8) The lens-fitted film unit of item 5, wherein a resistance value of the first resistor is in a range of 10 Kxcexa9-100 Kxcexa9.
(9) The lens-fitted film unit of item 1, wherein the oscillation transformer further having a tertiary winding, and the oscillation controlling circuit includes a serial connection of the tertiary winding and a parallel connection of a capacitor and a resistor.
(10) The lens-fitted film unit of item 1, further comprising: a charge indication element to indicate a charging state in the main-capacitor.
(11) The lens-fitted film unit of item 10, wherein the charge indication element is either a light emitting diode or a neon lamp.
(12) The lens-fitted film unit of item 1, wherein a value of the base potential for activating the oscillation transistor is higher than that for deactivating the oscillation transistor.
(13) A strobe circuit, comprising: a boosting-up circuit, which includes, a DC power source, an oscillation transistor, an oscillation transformer having a primary winding and a secondary winding, and a rectifying element for rectifying an electronic current induced at the secondary winding of the oscillation transformer; an oscillation controlling circuit for controlling a base potential of the oscillation transistor; and a strobe lighting circuit, which includes, a main-capacitor charged by the electronic current rectified by the rectifying element, and a strobe-lighting tube driven by an electronic charge charged in the main-capacitor, wherein a collector and an emitter of the oscillation transistor are serially coupled between the DC power source and the primary winding of the oscillation transformer, and a base of the oscillation transistor is connected to one end of the secondary winding of the oscillation transformer so as to apply a voltage, induced at the secondary winding, to the base, and the oscillation controlling circuit is coupled between the DC power source and the base of the oscillation transistor.
(14) The strobe circuit of item 13, wherein the oscillation controlling circuit includes a serial connection of a capacitor and a resistor.
(15) The strobe circuit of item 13, wherein the oscillation controlling circuit includes a serial connection of a second resistor and a parallel connection of a capacitor and a first resistor.
(16) The strobe circuit of item 13, wherein the oscillation transformer further having a tertiary winding, and the oscillation controlling circuit includes a serial connection of the tertiary winding and a parallel connection of a capacitor and a resistor.
(17) The strobe circuit of item 13, wherein a value of the base potential for activating the oscillation transistor is higher than that for deactivating the oscillation transistor.
(18) An oscillation circuit, comprising: a DC power source; an oscillation transistor; an oscillation transformer having a primary winding and a secondary winding; and an oscillation controlling circuit for controlling a base potential of the oscillation transistor; wherein a collector and an emitter of the oscillation transistor are serially coupled between the DC power source and the primary winding of the oscillation transformer, and a base of the oscillation transistor is connected to one end of the secondary winding of the oscillation transformer so as to apply a voltage, induced at the secondary winding, to the base, and the oscillation controlling circuit is coupled between the DC power source and the base of the oscillation transistor.
Further, to overcome the abovementioned problems, other oscillation circuits and strobe circuits, embodied in the present invention, will be described as follow:
(19) An oscillation circuit, characterized in that, in the oscillation circuit comprising an oscillation transistor, a collector and an emitter of which are serially coupled to a DC power supply and a primary winding of a oscillation transformer, and a base of which is driven by a voltage induced at the secondary winding of the oscillation transformer, an oscillation controlling circuit for controlling a base potential of the oscillation transistor is coupled.
(20) The oscillation circuit of item 19, characterized in that the oscillation controlling circuit is composed of a serial connection of a capacitor and a resistor.
(21) The oscillation circuit of item 19, characterized in that the oscillation controlling circuit is composed of a serial connection of a resistor and a parallel connection of a capacitor and a resistor.
According to the present invention, described in items 19-21, in a simple configuration added with the oscillation controlling circuit including a capacitor and a resistor, or a capacitor and two resistors, it becomes possible to provide an oscillation circuit, which makes it possible to conduct a timer operation for automatically stopping the oscillation circuit after a predetermined time has elapsed, and/or an intermittent oscillating operation, and which is suitably employed for lens-fitted film units incorporating strobe devices.
(22) A strobe circuit, characterized in that the strobe circuit comprises a oscillation circuit which includes a DC power supply and an oscillation transistor, a collector and an emitter of which are serially coupled to a DC power supply and a primary winding of a oscillation transformer, and a base of which is driven by a voltage induced at the secondary winding of the oscillation transformer, and which also includes a rectifying element, connected to the secondary winding of the oscillation transformer, for rectifying a boosted voltage boosted by the oscillation transformer, an oscillation controlling circuit, coupled between the DC power supply and the base of the oscillation transistor, for controlling a base potential of the oscillation transistor, and a strobe lighting circuit, which includes a main-capacitor charged by a voltage rectified by the rectifying element and a strobe-lighting tube driven by a charged voltage stored in the main-capacitor.
(23) The strobe circuit of item 22, characterized in that the oscillation controlling circuit is composed of a serial connection of a capacitor and a resistor.
(24) The strobe circuit of item 22, characterized in that the oscillation controlling circuit is composed of a serial connection of a resistor and a parallel connection of a capacitor and a resistor.
(25) The strobe circuit of item 22, characterized in that the oscillation controlling circuit is composed of a serial connection of a tertiary winding of the oscillation transformer and a parallel connection of a capacitor and a resistor.
(26) The strobe circuit, described in one of items 22-25 characterized in that the strobe circuit comprises a charge-notifying element for notifying the user of charging state of the main-capacitor.
(27) The strobe circuit of item 26, characterized in that, in the strobe circuit described in one of items 22-25, the charge-notifying element is selected out of either light emitting diodes or neon lamps.
According to the present invention, described in items 22-27, it is possible to reliably stop the oscillating action of the oscillation transistor by controlling the base potential of the oscillation transistor of the boosting-up circuit, under the operation of the oscillation controlling circuit composed of a combination of the capacitor, the resistor and the tertiary winding of the oscillation transformer, which are coupled between the DC power source and the base of the oscillation transistor. In addition, it is also possible to reduce the number of parts employed, resulting in the cost-reduction and the reduction of man-hours for assembling, and to surely prevent a power dissipation of the battery.
(28) The oscillation circuit, described in one of items 19-21, characterized in that a value of the base potential for activating the oscillation transistor is higher than that for deactivating the oscillation transistor.
(29) The oscillation circuit, described in one of items 22-26, characterized in that a value of the base potential for activating the oscillation transistor is higher than that for deactivating the oscillation transistor.